With the Fast Metabolism perk, the player character gains a 20% bonus when using stimpaks. In Hardcore mode, the multiplier increases the amount of healing per second making stimpaks an even better in-combat healing option. Players outside of Hardcore mode may be better served by simply applying multiple stimpaks from their Pip-Boy rather than investing in the perk.
This perk also affects (adapted) alien biogel, which is added to Fallout 3 with the Mothership Zetaadd-on.
Abominable ·Animal Control ·The Bear-Slayer ·Beautiful Beatdown ·Brainless/Big Brained ·Bug Stomper ·Camel of the Mojave ·Coin Operator ·Day Tripper ·Dead Man's Burden ·Dine and Dash ·Divide Survivor ·DNAgent ·DNAvenger ·Elijah's Ramblings ·Fast Times ·Free Radical ·Friendly Help ·Ghost Hunter ·Heartless/Cardiac Arrest ·Lonesome Road ·Lord Death ·Machine Head ·Marked ·Meat of Champions ·Melee Hacker ·Mutant Massacrer ·Power Armor Training ·Scourge of the East ·Set Lasers for Fun ·Sierra Madre Martini ·Spineless/Reinforced Spine ·Tough Guy
and a high Medicine skill.